This invention belongs to the broad realm of information technology and pertains more particularly to a method of, and apparatus for, editing or rewriting data such as, typically, compressed audio data with little or no adverse effect upon the sound quality.
A variety of data compression techniques have been suggested, and some of them have won more or less widespread commercial acceptance, among such commercially accepted ones being Moving Picture Coding Experts Group's MPEG-3 or, more simply, MP3. Patent Cooperation Treaty Publication No. WO90/13182 is hereby cited as describing how to create MP3-encoded data streams by the Huffman code. The MP3 data stream takes the form of a repetition of frames each constituted of a header section, a side data section, and a main data section.
Difficulties have been encountered with the MP3 encoding of digitized audio data. MP3 encoders on the market today are inherently capable of creating data streams at 320 kilobits per second (kbps) at a maximum, but now commonly put to use at a deplorably lower rate of 128 kbps. The maximum possible bit rate was determined because digital audio frames and MP3 frames agree in time at that rate; that is, the complete audio data in each audio frame could be contained in one MP3 frame if the audio data were MP3 encoded at the maximum bit rate. But then storage media of inordinately large capacities were required for storing the MP3-encoded audio data. Hence the currently preferred MP3 encoder bit rate of 128 kbps.
The MP3 encoding of audio data at this low bit rate had its own weaknesses, however. Depending upon the bit number, the data from each audio frame was rearranged not necessarily just in one MP3 frame but over two or three consecutive ones at that low bit rate, so that the audio data was not wholly rewritable or editable in the form of the MP3 data stream. Conventionally, this difficulty was literally circumvented by converting the MP3 encoded audio data into the known WAVE file format. After being edited in that format, the data was reconverted back into the MP3 format. The audio data that was conventionally processed in this manner inevitably suffered losses in sound quality for conversion from MP3 to WAVE format and reconversion from WAVE to MP3 format.